High frequency module and radio device using the same

ABSTRACT

The high-frequency module of the present invention is formed of two sections: first high-frequency circuit  5  having a first filter circuit; and second high-frequency circuit  6  having a second filter circuit. At least any one of the two high-frequency circuits has a conductive case. The structure is highly effective in attenuating a spurious signal, thereby solving the problem that the output level of the spurious signal fed from the high-frequency module is undesirably increased.

TECHNICAL FIELD

The present invention relates to a high-frequency module employed formobile communications and a wireless device using the high-frequencymodule.

BACKGROUND ART

In a high-frequency circuit, a spurious signal generated in a mixingcircuit and a matching circuit is removed by a filter circuit. Such ahigh-frequency circuit has conventionally been configured as a singlemodule. FIG. 6 shows a conventional high-frequency module. In theconventional high-frequency circuit block, mixing circuit 12 mixes abaseband signal fed from baseband section 31 with a local signal fedfrom oscillator 41. A spurious signal produced by mixing circuit 12 isattenuated by first filter 13 and second filter 22 of filter circuit 18.A desired high-frequency signal has thus been obtained.

In the prior-art high-frequency module, however, due to the structureconfigured in one module, a spurious signal produced by matching device14 connected to the input side of first filter 13 directly goes, withoutpassing through first filter 13, matching device 17, and second filter22, into matching device 24. In the module, matching device 17 isconnected to the output side of first filter 13 and the input side ofsecond filter 22, and matching device 24 is located to the output sideof second filter 22.

Therefore, in matching device 24, the spurious signal directly come frommatching device 14 has an output level greater than that of the spurioussignal given attenuation by first filter 13 and second filter 22,accordingly, the resultant spurious signal cannot maintain a desirableattenuation level. As a result, the output level of the spurious signalfed from the high-frequency module has undesirably increased.

DISCLOSURE OF THE INVENTION

The present invention addresses the problem above. It is therefore theobject to provide a high-frequency module capable of offering a spurioussignal with a preferably suppressed output level.

To achieve the object, the structure of the present invention has thehigh-frequency circuit formed of two sections: the first high-frequencycircuit having a first filter circuit, and the second high-frequencycircuit having a second filter circuit.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a high-frequency module of an exemplaryembodiment of the present invention.

FIG. 2 is an enlarged side view of the high-frequency module of theexemplary embodiment.

FIG. 3 is a top view of the high-frequency module of the exemplaryembodiment.

FIG. 4 is a circuit diagram of the high-frequency module of theexemplary embodiment.

FIG. 5 is a general block diagram of a wireless device employing thehigh-frequency module of the present invention.

FIG. 6 is a block diagram of a conventional high-frequency module.

DETAILED DESCRIPTION OF CARRYING OUT OF THE INVENTION

An exemplary embodiment of the present invention is describedhereinafter with reference to the accompanying drawings, FIG. 1 throughFIG. 4.

FIG. 1 is a perspective view of high-frequency module 100 of anexemplary embodiment of the present invention. High-frequency module 100of the present invention contains first high-frequency circuit 5 andsecond high-frequency circuit 6.

In first high-frequency circuit 5 of the present invention, mixingcircuit 12 and first filter circuit 16 are mounted on first circuitboard 201, and over which, metallic case 4 is fixed to cover them.

FIG. 2 shows an enlarged side view of high-frequency module 100. Edgeelectrode 7 is formed at the side of first circuit board 201. In thestructure, high-frequency noise is shielded by electrically connectingbetween the GND electrode of edge electrode 7 and terminal 3 formed onmetallic case 4 with solder 8.

On the other hand, in second high-frequency circuit 6 shown in FIG. 1,the second filter circuit is mounted on second circuit board 202. Likefirst high-frequency circuit 5, metallic case 4 covers components of thefilter circuit.

As shown in FIG. 3, which is a top view of the structure ofhigh-frequency module 100, first high-frequency circuit 5 and secondhigh-frequency circuit 6 are mounted on motherboard 1. Thehigh-frequency circuit of the present invention is configured byestablishing a high-frequency connection between the two circuitsthrough signal line 10 on motherboard 1.

The connecting line has an impedance of 50 ohm. GND pattern 9 is formedaround the signal line to protect the signal line from an effect ofnoise, whereby the characteristics of the high-frequency module ismaintained.

Now will be described how the high-frequency circuit of the presentinvention works, with reference to FIG. 4.

Base band section 31 outputs a 380 MHz base band signal; on the otherhand, oscillator 41 outputs a 1760 MHz local signal. The two signals areadded at mixer 12 to be resultant output of 2140 MHz. The resultantsignal passes through matching device 14 of first filter circuit 16 andenters into first filter 13. First filter 13 is a dielectric filter,which can substantially eliminate noise of a local signal, therebyattenuating the 2140 MHz spurious signal fed from mixer 12 by 50 dB tofeed the signal to matching device 15. In the structure, matching device14 is located to the input side of first filter 13; on the other hand,matching device 15 is located to the output side of first filter 13.Such an arrangement decreases radiation caused by unmatched impedance.As a result, the spurious signal, which is fed from the input side ofmatching device 14 and, without passing through first filter 13, fedinto matching device 15, is attenuated more than 60 dB. That is, firstfilter circuit 16 can constantly keep 50 dB attenuation.

Besides, as described above, covering first high-frequency circuit 11with metallic case 4 can suppress the spurious signal fed from thecircuit.

Next, the output signal from matching device 15 goes into matchingdevice 23, which forms second filter circuit 19 of second high-frequencycircuit 21. Given impedance matching by matching device 23, the outputsignal is fed into second filter 22. Second filter 22 is a dielectricfilter, which can substantially eliminate noise of a spurious signal,thereby attenuating the 380 MHz spurious signal fed from mixer 12 by 50dB to feed the signal to matching device 24. In second high-frequencycircuit 21, matching device 23 is located to the input side of secondfilter 22; on the other hand, matching device 24 is located to theoutput side of second filter 22. Such an arrangement decreases radiationcaused by unmatched impedance. As a result, the spurious signal from thelocal signal, which is fed from matching device 23 and, without passingthrough second filter 22, fed into matching device 24, is attenuatedmore than 60 dB. On the other hand, the spurious signal generated by thelocal signal fed into matching device 24 directly from matching device14 of first high-frequency circuit 11, without traveling through firstfilter 13, matching devices 15 and 23, and second filter 22, isattenuated more than 110 dB. As a result, second filter circuit 19 canconstantly keep 50 dB attenuation.

With the structure of first high-frequency circuit 11 and secondhigh-frequency circuit 21, a desired amount of attenuation, i.e., 100 dBattenuation of the spurious signal can be achieved.

Although the explanation above introduces the structure in whichhigh-frequency module 100 employs a matching device, it is not limitedthereto; an amplifier and an isolator can be used with the matchingdevice to obtain the similar effect.

Although the explanation above introduces a structure employing a singlemixer, it is not limited thereto; a structure having two or more mixerscan provide the similar effect.

Although the explanation above introduces a structure employingdielectric filters for filter 13 and filter 22, it is not limitedthereto; a high-frequency module employing filters with an excellentquality in eliminating noise, such as a surface acoustic wave (SAW)filter and a MEMS filter, can provide the similar effect.

Although the explanation above introduces a structure employing twofilters, it is not limited thereto; a high-frequency module having threeor more filters can provide the similar effect.

Although the explanation above introduces a structure employing twohigh-frequency circuits, it is not limited thereto; a structure havingthree or more circuits can provide the similar effect.

Although the explanation above introduces a structure in which a baseband signal fed from base band section 31 has a frequency of 380 MHz,and a local signal has a frequency of 1760 MHz, it is not limitedthereto; a structure in which a local signal has a frequency rangingfrom 1730 to 1790 MHz can provide the similar effect.

Although the explanation above introduces a structure in which a baseband signal fed from base band section 31 has a frequency of 380 MHz,and a local signal has a frequency of 1760 MHz, it is not limitedthereto; a structure in which a base band signal has a frequency rangingfrom 10 to 400 MHz can provide the similar effect.

FIG. 5 shows wireless device 61 employing high-frequency module 100 ofthe present invention. In the structure, a base band signal fed frombase band section 31 and a local signal fed from oscillator 41 are fedinto first high-frequency circuit 11 to have frequency conversion. Thesignal from circuit 11 passes through second high-frequency circuit 21and front-end section 62 and goes out from antenna 63 into the air. Thewireless device employing high-frequency module 100 of the presentinvention is highly effective in attenuating a spurious signal,accordingly, the spurious signal radiated from antenna 63 is preferablysuppressed. The wireless device capable of suppressing a spurious signalto a low level can thus be obtained.

INDUSTRIAL APPLICABILITY

According to the structure of the present invention, as described above,the high-frequency circuit is divided into two sections: a firsthigh-frequency circuit having a first filter circuit, and a secondhigh-frequency circuit having a second filter circuit. With thestructure, a high-frequency module capable of suppressing the output ofa spurious signal can be obtained.

1. A high-frequency module comprising: a) a first high-frequency circuitincluding: a-1) a mixing circuit for mixing a base band signal fed froma base band section with a local signal fed from an oscillator; and a-2)a first filter circuit for attenuating a local leak from the mixingcircuit; and b) a second high-frequency circuit containing a secondfilter circuit for attenuating a local leak from the first filtercircuit, wherein at least any one of the first high-frequency circuitand the second high-frequency circuit is covered with a conductive case.2. The high-frequency module of claim 1, wherein the conductive case ismade of metal.
 3. The high-frequency module of claim 1, wherein theconductive case is formed of i) an insulating resin for covering thecircuits, and ii) metal plating for covering a surface of the insulatingresin.
 4. The high-frequency module of claim 1, wherein the first filtercircuit and the second filter circuit include a dielectric filter. 5.The high-frequency module of claim 1, wherein a signal line with animpedance of 50Ω connects between the first high-frequency circuit andthe second high-frequency circuit.
 6. The high-frequency module of claim1 further includes a motherboard, on which a first circuit boardcontaining the first high-frequency circuit, a second circuit boardcontaining the second high-frequency circuit, and the 50Ω-signal lineconnecting between the first high-frequency circuit and the secondhigh-frequency circuit are mounted.
 7. A wireless device employing ahigh-frequency module, the high-frequency module comprising: a) a firsthigh-frequency circuit further including: a-1) a mixing circuit formixing a base band signal fed from a base band section with a localsignal fed from an oscillator; and a-2) a first filter circuit forattenuating a local leak from the mixing circuit; and b) a secondhigh-frequency circuit containing a second filter circuit forattenuating a local leak from the first filter circuit, wherein at leastany one of the first high-frequency circuit and the secondhigh-frequency circuit is covered with a conductive case.
 8. Thewireless device of claim 7, wherein the high-frequency module includes amotherboard, on which a first circuit board containing the firsthigh-frequency circuit, a second circuit board containing the secondhigh-frequency circuit, and the 50Ω-signal line connecting between thefirst high-frequency circuit and the second high-frequency circuit aremounted.